Hot box process for preparing foundry shapes with certain aqueous phenolic resin solutions

ABSTRACT

This invention relates to heat curable foundry mixes and binder compositions particularly suitable for making foundry shapes by a hot box process. The binders used are aqueous basic solutions of phenolic resole resins. Salts are added to the binders or the sand to improve the tensile strength of foundry shapes made with the foundry mixes. Silicone compounds are added to the aggregate to improve the water resistance of foundry shapes made with the foundry mixes containing the binder and salt. The foundry shapes are used to prepare metal castings.

This application is a division of application No. 90,803, filed Aug. 28,1987, now U.S. Pat. No. 4,789,693.

TECHNICAL FIELD

This invention relates to heat curable foundry mixes and bindercompositions particularly suitable for making foundry shapes by a hotbox process. The binders used are aqueous basic solutions of phenolicresole resins. Salts are added to the binders or the aggregate toimprove the tensile strength of foundry shapes made with the foundrymixes. Silicone compounds are added to the aggregate to improve thewater resistance of foundry shapes made with the foundry mixescontaining the binder and salt. The foundry shapes are used to preparemetal castings.

BACKGROUND

It is known that heat curable workable foundry shapes can be prepared bythe so-called "hot box" process. This process involves injecting amixture of a foundry aggregate containing an acid-generating curingcatalyst and a thermosetting resin into a heated corebox where it isallowed to harden into a workable foundry shape, which is then removedfrom the corebox. Curing according to this process takes place in anacidic medium. The use of this process can, depending upon the choice ofcatalyst and resin, cause the formation of undesirable smoke and fumesdue to the generation of free phenol and free formaldehyde, as well asthe generation of significant amounts of nitrogen which can result inthe formation of casting defects (pinholes) when metal castings areprepared. This process also requires that the acid-generating curingcatalyst and thermosetting resin be mixed with the aggregate as separatecomponents.

SUMMARY OF THE INVENTION

The subject invention relates to heat curable foundry mixes comprising:

a. a foundry aggregate;

b. an effective binding amount of a binder comprising an aqueous basicsolution of a phenolic resole resin wherein said aqueous basic solutionhas

(i) a viscosity of less than about 850 centipoise at 25° C.;

(ii) a solids content of about 35 to about 75 percent by weight, saidweight based upon the total weight of the basic solution; and

(iii) an equivalent ratio of base to phenolic compound of about 0.2:1.0to 1.1:1.0; and

c. a salt in amount which will increase the tensile strength of thefoundry shapes prepared with said binder.

The salt can be added directly to the binder in some cases as will beexplained later. Usually it is added as an aqueous solution to theaggregate. The addition of the salt improves the tensile strength offoundry shapes made with the foundry mixes.

For applications where water resistance is important, a silicone fluidor emulsion is added to the aggregate before applying the binder andsalt to it. It has been found that this causes the foundry shapes to bemore water resistant.

With the proper selection of the salt, it is possible to improve tensilestrengths of the workable foundry shapes without introducing compoundswhich will form nitrogen, undesirable smoke, and fumes. Many of thesalts are inexpensive and do not add significant costs to themanufacturing process.

The foundry mixes are shaped and then cured by heating in a convectionoven, microwave oven, or other heat source. Nevertheless, curing isgenerally carried out by a hot box process. However, in contrast to thetraditional hot box process, where curing takes place in an acidicmedium, the binders used herein are cured under basic conditions sincethe binder solution is highly basic (a pH of 9-13, usually a pH of11-13) and the addition of the salt does not significantly affect thepH.

Other aspects of the invention relate to the process of preparingfoundry shapes with the foundry mixes; the foundry shapes prepared withthe mixes; the process of casting metal parts using the foundry shapes;and the metal casting prepared with the foundry shapes. The foundrymixes are particularly useful for making foundry shapes by a hot boxprocess.

BEST MODE AND OTHER MODES FOR CARRYING OUT THE INVENTION

For purposes of describing and claiming this invention, the term"binder" will refer to the aqueous basic solution of phenolic resoleresin. The binder is highly basic and generally has a pH of from 9 to13, usually from 11 to 13. The term "binder composition will refer to amixture of the binder, an inorganic salt", and other optional additivessuch as silanes, siloxanes, bench life extenders, release agents, etc.The term "foundry shape" includes foundry molds and cores made fromfoundry mixes.

The aggregate used to prepare the foundry mixes is that typically usedin the foundry industry for such purposes or any aggregate that willwork for such purposes. Generally, the aggregate will be sand whichcontains at least 70 percent by weight silica. Other suitable aggregatematerials include zircon, olivine, alumina-silicate sand, chromite sand,and the like. Generally, the particle size of the aggregate is such thatat least 80 percent by weight of the aggregate has an average particlesize between 50 and 150 mesh (Tyler Screen Mesh).

As was mentioned, the binder is an aqueous basic solution of phenolicresole resin. The resin used in the solution is prepared by methods wellknown in the foundry art. The general procedure involves reacting anexcess of aldehyde with a phenolic compound in the presence of a base attemperatures of about 50° C. to 120° C., typically from 70° C. to 100°C., to prepare a phenolic resole resin. Generally the reaction will alsobe carried out in the presence of water. The resulting phenolic resoleresin is diluted with a base and/or water so that an aqueous basicsolution of the phenolic resole resin results having the followingcharacteristics:

1. a viscosity of less than about 850 centipoise, preferably less thanabout 450 centipoise at 25° C. as measured with a Brookfield viscometer,spindle number 3 at number 12 setting;

2. a solids content of 35 percent by weight to 75 percent by weight,preferably 50 percent by weight to 60 percent by weight, based upon thetotal weight of the aqueous basic solution, as measured by a weight lossmethod by diluting 0.5 gram of aqueous resole solution with onemilliliter of toluene and then heating on a hotplate at 150° C. for 15minutes; and

3. an equivalent ratio of base to phenol of from 0.2:1 to 1.1:1.0,preferably from 0.3:1.0 to 0.95:1.0.

As an alternative to the procedure outlined, it may be possible toprepare the aqueous basic solutions by dissolving all of the base inphenol and then reacting with formaldehyde until the desired propertiesare achieved.

It has been found that aqueous basic solutions having viscositiesoutside the cited range are difficult to use in hot box equipment.Aqueous basic solutions with a solids content below the cited range willnot sufficiently coat the aggregate while those having a solids contentabove the cited range will not be sufficiently flowable in the moldingequipment. The equivalent ratio specified for the base relates to theneed for having solutions which have adequate shelf stability.

Although these ranges have been specified, it should be pointed out thatit is not claimed that these aqueous basic solutions are novel products,or that the ranges are critical. The ranges are set forth to provideguidelines for those who want to make and use the invention. Obviously,the invention will usually be practiced more effectively in thepreferred ranges specified. With this in mind, more specific procedureswill be set forth for for preparing phenolic resole resins.

The phenolic compounds used to prepare the phenolic resole resins can berepresented by either of the following structural formulae: ##STR1##wherein A, B, and C are individually selected from the group consistingof hydrogen, hydrocarbon radicals, hydroxy, and halogen in formula I,and R in formula II is hydrogen or a methyl radical.

The aldehyde used in preparing the phenolic resole resin may also varywidely. Suitable aldehydes include aldehydes such as formaldehyde,acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. Ingeneral, the aldehydes used have the formula RCHO, where R is a hydrogenor a hydrocarbon radical of 1 to 8 carbon atoms. The most preferredaldehyde is formaldehyde.

The basic catalysts used in preparing the phenolic resole resin includebasic catalysts such as alkali or alkaline earth hydroxides, and organicamines. The amount which is used depends upon the specific propertiesdesired and the process utilized. Those skilled in the art are familiarwith these amounts.

It is possible to add modifiers such as lignin and urea when preparingthe phenol-formaldehyde resole resins as long as the amount is such thatit will not detract from achieving the desired properties of the aqueousbasic solutions. Often the urea is added as a scavenger to react withunreacted formaldehyde and remove the odor caused by it.

The phenolic resole resins used in the practice of this invention aregenerally made from phenol and formaldehyde at a mole ratio offormaldehyde to phenol in the range of from about 1.1:1.0 to about3.0:1.0. The most preferred mole ratio of formaldehyde to phenol is amole ratio in the range of from about 1.4:1.0 to about 2.2:1.0.

As was mentioned previously, the phenolic resole resin is either formedin the aqueous basic solution, or it is diluted with an aqueous basicsolution. The base used in the aqueous basic solution is usually analkali or alkaline earth metal hydroxide such as potassium hydroxide,sodium hydroxide, calcium hydroxide, or barium hydroxide, preferablypotassium hydroxide. It should again be mentioned that the aqueous basicsolutions of phenolic resole resins described herein are not novelproducts, nor is their preparation. The parameters set forth pertainingto their preparation are merely guidelines for those who want to makethe aqueous basic solutions of phenolic resole resins. There may beother ways to make them not described herein.

The binder is used in an effective binding amount. An effective bindingamount is amount which will impart adequate tensile strengths to thefoundry shapes, when used in conjunction with the inorganic salt, forthe particular uses of the foundry shapes. Generally, an effectivebinding amount of the binder is from 0.5 weight percent to 7.0 weightpercent, based upon the weight of the aggregate, usually from 1.0 weightpercent to 3.0 weight percent of binder.

The salts used in the foundry mix to improve the tensile strength of thefoundry shapes made with the foundry mix are inorganic or organic salts.They are usually added to the aggregate as aqueous solutions. However,salts which are compatible with the binder can be added directly to thebinder. Salts which are compatible with the binder are those which willnot react with the binder to form insoluble products. Such salts alsoprovide binder compositions which are predominately homogeneous. Thesesalts have the advantage of enabling the formulator to package, sell,and disperse the mixture of binder and salt in one container.

In general the potassium and sodium salts of inorganic acids,particularly mineral acids such as hydrochloric acid, sulfuric acid, andnitric acid, are more compatible with the binder. On the other hand,multivalent metal salts such as ZnSO₄, CuSO₄, NiSO₄, Mn(NO₃)₂, SnCl₄,Al(NO₃)₃, and the like are not compatible with the binder.

Although the salts can be added directly to the binder or aggregatedepending upon their compatibility with the binder, another way ofgetting the salt into the binder is by forming it in situ. This is doneby adding a solution of an acid, which is capable of forming a salt, tothe binder or aggregate. Generally used as the acid is an inorganic acidsuch as a mineral acid, for example sulfuric acid, nitric acid, andhydrochloric acid.

The amount of salt or salt forming acid used is an amount sufficient toincrease the tensile strength of the foundry shapes made with thefoundry mix containing the binder and salt. Generally, this amount isfrom 1 to 10 weight percent based upon the weight of the binder,typically from 3 to 7 weight percent. When a dilute solution of the saltor acid is used (such a 10 to 50 percent solution in water, typically a20 to 30 percent solution in water), from 10 percent to 50 percent byweight of the solution, is used based upon the weight percent of thebinder, typically from 20 to 50 percent by weight. Obviously theseweight percentages are not absolute guidelines. The amount chosen by oneskilled in the art will depend upon the pH of the resin, the solidscontent of the resin, the dilution and equivalency of the salt added,and concentration of the acid if one is used.

Although not required to improve the tensile strengths of foundry shapesmade with the binder and salt, it is preferable to use a siliconecompound where the foundry shape must show a higher degree of resistanceto water. In such cases the water may come from moisture in the air orspecial processing conditions of the foundry shapes, such as immersionin a core wash. The addition of a silicone compound to the foundry mixcontaining the binder and salt improves the resistance of the foundryshape to moisture.

Silicone compounds, which can be used in the foundry mix to improve thewater resistance of the foundry shapes made with the foundry mix,typically are polydimethylsiloxanes, often trimethylsilyl terminated.Generally, they are sold commercially as fluids or emulsions (whichcontain water and a surfactant as well as the silicone compound).Examples of commercially available products which contain siliconecompounds and are effective include DC 1101, DC 108, DC 24, DC 531. Allof these mentioned products are emulsions except DC 531, and all aresold by Dow Corning Corporation. Examples of other commerciallyavailable silicone compounds are LE-460, AF-70 which are sold by UnionCarbide and General Electric respectively.

The silicone compound is preferably mixed with the foundry aggregatebefore the binder and salt are added to the aggregate. The amount ofsilicone compound used in the foundry mix is an amount effective to makefoundry shapes prepared with the mix more resistant to water. Generallythis will be from 0.01 to 1.0 weight percent based upon the weight ofthe sand, more typically from 0.05 to 0.1 weight percent. Since siliconecompounds are expensive, one would not generally used more than wasessential for the particular application.

It will be apparent to those skilled in the art that other additivessuch as silanes, benchlife extenders, release agents, solvents, etc. canbe used and may be added to the binder composition, aggregate, orfoundry mix.

Curing can be accomplished by heating the shape foundry mix in aconvection oven, a microwave oven, or by means of another heat source.Generally, however, curing is accomplished by injecting the foundry mixinto a core box which has been heated to a temperature sufficient tocure the foundry mix and produce a workable foundry shape. Generally,the temperature needed to cure the foundry mix is from 200° C. to 300°C., preferably from 230° C. to 260° C. A workable foundry shape is onewhich can be handled without breaking. Generally, the foundry mix mustreside in the core box from 15 seconds to 120 seconds, usually from 30seconds to 90 seconds to produce a workable foundry shape.

Metal castings can be prepared from the workable foundry shapes bymethods well known in the art. Molten ferrous or non-ferrous metals arepoured into or around the workable shape. The metal is allowed to cooland solidify, and then the casting is removed from the foundry shape.

EXAMPLES

The examples which follow will illustrate specific embodiments of theinvention. They are not intended to imply that the invention is limitedto these embodiments. The temperatures in the examples are in degreesCentigrade and the parts are parts by weight unless otherwise specified.

In the examples, the following binder was used to the prepare thefoundry mixes:

A 1:1.7 phenol-formaldehyde base catalyzed resole condensate having a pHof approximately 9.0 is prepared by warming a stirred mixture of 30.0parts of phenol, 32.6 parts of 50% formaldehyde solution, 8.2 parts ofwater and 2.3 parts of methanol to 83° C. To this mixture is added 0.9parts of 50% sodium hydroxide solution and the temperature is allowed toexotherm, but not exceed 83° C. After the exotherm has subsided, 0.9parts of 50% sodium hydroxide solution is added and the temperature isheld at 83° C. for 2 hours. The mixture is then cooled to 70° C. and 3.5parts of 50% potassium hydroxide solution is added over 15 minutes whileallowing the temperature to rise to 83° C., applying heat whennecessary. The reaction is continued at 83° C. until a refractive indexof 1.4848 is reached, then is cooled to 60° C. and 21.2 parts of a 50%potassium hydroxide solution is added and agitation is continued for 10minutes at 60° C. before cooling to room temperature. The resultingresole solution has a percent solids content of 50-53% and a viscosityof 110-180 c.p.s. @25° C. The resole solution has an equivalent ratio ofbase to phenol of about 0.76:1.

Foundry mixes were prepared as indicated in the examples. In all of theexamples Manley 1L5W sand was used. The amount of binder used was twoweight percent based upon the weight of the sand (BOS).

The resulting foundry mixes were forced by air blowing the mix into astandard AFS core box (dog bone shape) which had been heated to atemperature of 232° C. The tensile strengths (in psi) for varioussamples were measured after being taken from the core box at specifieddwell times (dwell times were 60 and 90 seconds in most cases). The hottensile measurements were taken within 10 seconds after removing theshapes from the corebox. The cold tensiles were measured at least 1 hourafter removing the shapes from the corebox and storing them at arelative humidity of approximately 50 percent. Tensile measurements werealso made 24 hours after being taken from the corebox, and 24 hoursafter being taken from the corebox and being exposed to relativehumidity of 100 percent for 1 hour (24+1).

EXAMPLES 1-7

Examples 1-7 illustrate the effect of using a salt in the foundry mix onthe tensile strengths of foundry cores prepared with the foundry mix.The tensile strength is first shown for a foundry mix without a salt(Control #1). In Examples 2-5 a 20 percent aqueous solution of the saltwas mixed with the aggregate, while Examples 1 and 6 used a 30 percentaqueous solution. The solution was used in an amount of 20 percent byweight based upon the weight of the binder. Control #2 was neededbecause the experiments with the hydroxylamine sulfate were carried outon a different day.

In comparison Example A, Example 6 is repeated except 0.066 percent byweight (based upon the weight of the aggregate) of a silicone compound,DC 1101, is added to the aggregate before mixing in the bindercomposition. In comparison Example B, comparison Example A is repeatedexcept no salt is used. The results are shown in Table I.

The results of Example 1-6 show that the use of a salt in the foundrymix increases the tensile strength of cores made with the foundry mix,particularly the cold tensile strengths and the tensile strengthsmeasured 24 hours after being removed from the core box. Theseexperiments suggest that the addition of the silicone compound does notimprove tensile strengths in the presence or absence of the salt.

                                      TABLE I                                     __________________________________________________________________________    (Results of Core Making Tests Using                                           Foundry Mixes with a Salt)                                                                         Tensiles                                                                                           24 + 1                                                   Hot   Cold   24 hr.  100%                                                     Dwell (sec)                                                                         Dwell (sec)                                                                          Dwell (sec)                                                                           Dwell (sec)                         Example Salt Used    60 90 60  90 60  90  60                                                                              90                                __________________________________________________________________________    Control #1                                                                            None         89 125                                                                              141 165                                                                              60  60  36                                                                              43                                1       NH.sub.2 OH.HCl                                                                            95 108                                                                              155 273                                                                              118 117 58                                                                              62                                2       NaCl         78 134                                                                              177 257                                                                              78  114 42                                                                              53                                3       CH.sub.3 COONa                                                                             71 109                                                                              151 231                                                                              63  83  54                                                                              63                                4       CuSO.sub.4   77 126                                                                              144 168                                                                              71  86  33                                                                              44                                5       ZnSO.sub.4   73 100                                                                              170 223                                                                              86  120 41                                                                              63                                Control #2                                                                            none         75 118                                                                              99  194                                                                              77  91  50                                                                              73                                6       NH.sub.2 OH.H.sub. 2 SO.sub.4                                                              73 118                                                                              138 281                                                                              123 157 62                                                                              101                               Comparison A                                                                          NH.sub.2 OH.H.sub. 2 SO.sub.4 /DC 1101                                                     69 107                                                                              131 213                                                                              122 149 60                                                                              88                                Comparison B                                                                          no salt/only DC 1101                                                                       62 103                                                                              123 114                                                                              63  79  38                                                                              102                               __________________________________________________________________________

EXAMPLES 7-10

Examples 7-10 illustrate the effect on the water resistance of the coresof adding a silicone compound to a foundry mix containing a salt. Thetensile strength is first shown for a foundry mix containing no salt andno silicone (Control #3). In all of the examples the silicone compoundwas DC 1101 sold by Dow Corning. It was added directly to the aggregatebefore adding the binder and salt. The amount of silicone used inExamples 7-10 was 0.066 weight percent based upon the weight of theaggregate. In these examples, a salt solution was added to the aggregatein an amount of 20 weight percent based upon the weight of the binder.

The following test was used to determine the water resistance of thecores:

CORE WASH TEST

In order to improve the core's performance when making metal castings,it is common practice to dip the cores in a core wash solution. Thecorewash used for testing the cores in these tests is a mixture ofwater, graphite, and ceramic materials having a specific gravity of 32°Be (Baume).

The cores are prepared by allowing them to dwell in the corebox for 80seconds at a temperature of 232° C. After cooling for one half hour, thetensile strength of the standard (STD) is measured. Another sample isdipped in and out of the core wash, baked at 450° F. for 30 minutes,stored at room temperature for 60 minutes, and then the tensile strengthis measured.

The results of the core wash test are shown in TABLE II. The tensilestrengths of the cores are shown before and after dipping them in thecore wash. If the cores do not crumble and disintegrate after beingdipped, they show satisfactory water resistance.

                                      TABLE II                                    __________________________________________________________________________    (Results of Core Making Tests Using                                           Foundry Mix with Salt and Silicone)                                                         Concentration of                                                                         Tensile (psi)                                                                        Tensile (psi)                                 Example                                                                             Salt Used                                                                             Salt Solution (wt. %)                                                                    Before Dip                                                                           After Dip                                     __________________________________________________________________________    Control #3                                                                          none    none       230    crumbled                                      7     NH.sub.2 OH.H.sub. 2 SO.sub.4                                                         30         329    104                                           8     NH.sub.4 NO.sub.3                                                                     54         317    123                                           9     (NH.sub.4).sub.2 SO.sub.4                                                             30         154    121                                           10    NH.sub.4 Cl                                                                           20         270    74                                            __________________________________________________________________________

Examples 11-14 show that the DC1101 silicone emulsion makes cores,containing the salt, more water resistant. TABLE III which followssummarizes the results of experiments carried out under conditionssimilar to those used in Examples 7-10 except different siliconecompounds were used. These examples indicate that the silicones used inthese examples were effective at improving the water resistance of thecores which contained the salt and silicone. The salt used in all oftheses examples was hydroxylamine sulfate. Control #4 did not contain asalt or a silicone compound.

                  TABLE III                                                       ______________________________________                                        (Results of Core Making Tests Using                                           Foundry Mix with Salt and Silicone)                                                                Tensile (psi)                                                                             Tensile (psi)                                Example Silicone Used*                                                                             Before Dip  After Dip                                    ______________________________________                                        Control #4                                                                            None         273         crumbled                                     11      DC1101       323         90                                           12      DB110A       266         29                                           13      LE460HS      355         121                                          14      SM2155       312         127                                          ______________________________________                                         DB110A  a silicone compound sold by Dow Corning.                              LE460HS  a silicone compound sold by Union Carbide.                           SM2155  a silicone compound sold by General Electric.                    

EXAMPLES 15-17

These examples were carried out under similar conditions to Examples7-14 except that in Example 15 a 20 percent salt solution of Na₂ SO₄ wasadded directly to the binder instead of the aggregate, and in Examples16 and 17 HCl (10% aqueous solution) and H₂ SO₄ (20% aqueous solution)were respectively added to the aggregate to form the salt in situ. Theresults of these experiments are summarized in TABLE IV.

                  TABLE IV                                                        ______________________________________                                                     Tensile (psi)                                                                            Tensile (psi)                                         Example      Before Dip After Dip                                             ______________________________________                                        15           271        45                                                    16           168        79                                                    17           167        77                                                    ______________________________________                                    

Examples 15-17 illustrate that the salt can be added directly to thebinder or it can be formed in situ by adding an acid to the aggregate.

We claim:
 1. A process for preparing a workable foundry shapecomprising:a. heating a foundry mix in a corebox at a temperaturesufficient to form a workable foundry shape wherein said foundry mixcomprises:(1) a foundry aggregate; (2) an effective binding amount of abinder comprising an aqueous basic solution of a phenolic resole resinwherein said aqueous basic solution hasi. a viscosity of less than about850 centipoise at 25 degrees Celsius; ii. a solids content of about 35to about 75 percent by weight, said weight based upon the total weightof the basic solution; and iii. an equivalent ratio of base to phenoliccompound of about 0.2:1.0 to 1.1:1.0; and (3) an inorganic salt in anamount effective to increase the tensile strength of the foundry shapesprepared with said foundry mix; and b. removing said workable shape fromthe corebox.
 2. The process of claim 1 wherein said binder is preparedwith a phenolic resin wherein the equivalent ratio of base to phenoliccompound used in preparing the binder is from 0.3:1.0 to 0.95:1.0 andthe phenolic compound used to prepare the binder is represented by thefollowing structural formula: ##STR2## wherein A, B, and C areindividually selected from the group consisting of hydrogen, hydrocarbonradicals, and halogen.
 3. The process of claim 2 wherein the basecatalyst used to prepare the phenolic resin of the binder is selectedfrom the group consisting of sodium hydroxide, potassium hydroxide, andmixtures thereof.
 4. The process of claim 3 where the viscosity of thebinder is from less than about 450 centipoise at 25 degrees Celsius. 5.The process of claim 4 wherein the phenolic resole resin of the binderis prepared by reacting formaldehyde and phenol in a mole ratio offormaldehyde to phenol of about 1.1:1.0 to about 2.2:1.0 in the presenceof an effective amount of a basic catalyst at elevated temperatures ofabout 50 degrees Celsius to about 120 degrees Celsius.
 6. The process ofclaim 5 wherein the salt of the binder is used as an aqueous solution.7. The process of claim 6 wherein the salt solution is an aqueoussolution of a multivalent metal salt.
 8. The process of claim 6 whereinthe salt is a sodium, potassium, ammonium, or hydroxylamine salt of aninorganic acid.
 9. The process of claim 8 wherein a salt solution ismixed with the foundry aggregate before the binder is mixed with theaggregate.
 10. The process of claim 9 wherein the salt solution is usedin an amount such that salt is present in amount of from 1 to 10 percentbased upon the weight of the binder.
 11. The process of claim 9 whereinthe salt solution is used in an amount such that salt is present inamount of from 3 to 7 percent based upon the weight of the binder. 12.The process of claim 11 wherein a silicone compound is mixed with thefoundry aggregate, in an amount effective to increase the waterresistance of the foundry shapes prepared with the foundry mix.
 13. Theprocess of claim 12 wherein the silicone compound is applied as a fluidor emulsion.
 14. The process of claim 13 wherein the silicone compoundis a polydimethyl siloxane.
 15. The process of claim 14 wherein thepolydimethyl siloxane is used in an amount of 0.01 to 0.5 weightpercent, based upon the weight percent of the aggregate.
 16. The processof claim 8 wherein the inorganic acid is sulfuric acid or hydrochloricacid.
 17. The process of claim 16 wherein the salt solution is formed insitu by the addition of the acid to the binder or the aggregate.
 18. Theprocess of claim 17 wherein the salt solution is used in an amount suchthat salt is present in amount of from 1 to 10 percent based upon theweight of the binder.
 19. The process of claim 16 wherein a saltsolution which is compatible with the binder is premixed with the binderbefore mixing with the aggregate.
 20. The process of claim 19 whereinthe salt solution is used in an amount such that amount of salt added tothe binder is from 1 to 10 weight percent based upon the weight of thebinder.
 21. The process of claim 19 wherein the salt solution is used inan amount such that salt is present in amount of from 3 to 7 percentbased upon the weight of the binder.
 22. The process of claim 21 whereina silicone compound is mixed with the foundry aggregate, prior to mixingthe binder with the foundry aggregate, in an amount effective toincrease the water resistance of the foundry shapes prepared with thefoundry mix.
 23. The process of claim 22 wherein the silicone compoundis applied as a fluid or emulsion.
 24. The process of claim 23 whereinthe silicone compound is a polydimethyl siloxane.
 25. The process ofclaim 24 wherein the polydimethyl siloxane is used in an amount of 0.01to 0.5 weight percent, based upon the weight percent of the aggregate.